1. Field of the Invention
This invention relates to smoking articles, such as cigarettes, for example, and methods of producing such articles.
2. Brief Description of the Related Art
The reduction of sidestream smoke produced by smoking articles has been a recent objective in the tobacco industry. Conventional methods thus far have centred on the identification and addition of sidestream reducing compounds either into the paper structure at the paper making stage or by coating of water-soluble sidestream reducing compounds onto the paper after manufacture; for example U.K. Patent Specification No. 2 139 869. The use of paper filler substances, such as magnesium oxide, in combination with low levels of alkali metal salts have also been proposed in U.S. Pat. No. 4,231,377. A more recent development has been the achievement of reduced sidestream smoke deliveries by providing a cigarette with a circumference within a range of 10 mm to 19 mm, a free burn rate of 25 mg min.sup.-1 to 50 mg min.sup.-1, and a tobacco packing density of 150 mg cm.sup.-3 to 350 mg cm.sup.-3 as has been disclosed in U.K. Patent Specification No. 2 175 789B.
In the past, cigarettes have been proposed having an inner core or filament surrounded by a layer of tobacco material. British Patent Specification No. 2 070 409 discloses a lengthwise extending filament which may be of an expanded reconstituted tobacco material treated with smoke-modifying agent. British Patent Specification No. 2 119 628 discloses a lengthwise extending line of expandable tobacco paste within a rod of cut tobacco material. The rod is heated and the tobacco line expands, compressing the tobacco thereabout. Lower density packing levels of the annulus of conventional tobacco material can thus be obtained.
French Patent Specification No. 998.556 discloses an inner core consisting of low quality tobacco and an annular layer of higher quality tobacco than the core. Savings in material costs are said to be achieved from such an arrangement. Further embodiments of coaxial cigarettes are described in French Patent Specification No. 1.322.254 and U.S. Pat. Nos. 1,829,559 and 4,716,913.
Cigarettes having a wrapped core are also known from U.S. Pat. No. 3,190,287, which relates to providing a by-pass arrangement in the smoking material rod for the mainstream smoke, and British Patent Specification No. 1 228 747, which relates to the selective filtration of polycyclic hydrocarbons from the mainstream smoke.
None of these documents deal with the concept of reducing sidestream smoke components of a combustible smoking article.
More recently, German Patent Application No. P38 36 210 disclosed a coaxial plain cigarette having an inner core of predominantly residue-free smoulderable material, especially tobacco, with a wrapper for the inner core, and an outer layer of tobacco and/or non-tobacco material coaxially surrounding the inner core and its wrapper, with a wrapper for the outer layer. The characteristics of the paper and tobacco rods are balanced to ensure a lower smoulder rate than in conventional cigarettes (less than 2 mm/min). Consequently a reduction in the amount of sidestream smoke produced per unit of time occurs during the inter puff period. However, the cigarette burns continuously in a conventional manner with a glowing coal, i.e. there is no part of the cigarette which is extinguished or extinguishes during puffing or smoulder.
Very recently, European Patent Application No. 0 380 324 disclosed a rod of smoking material wrapped in a wrapper and having extending coaxially therealong, over a great proportion of the rod length, a rod of activated carbon. The purpose of this rod, it is asserted, is to provide a clean-burning smoulder element which maintains free smoulder whilst the surrounding tobacco material extinguishes. As an alternative to the axial rod, a sheath wrapper also composed of activated carbon, can be used to enclose a conventional tobacco rod. The smoking material annulus or tobacco rod extinguishes in the inter-puff period and is re-ignited by the increased burning of the smoulder element due to the drawing in of oxygen when the cigarette is puffed upon. A drawback of this proposal is that the carbon element will have a disadvantageous effect on the mainstream carbon monoxide delivery. Also, it is to be expected that there would be an unacceptable carbon off-taste in the mainstream smoke delivered to the smoker. Furthermore, because of the fragile nature of the carbon rod, it may easily be broken during manufacture. The position of the carbon rod so that it cannot be seen by the smoker at the lighting end of the cigarette, in order to present a conventional rod end to the smoker, will also make for manufacturing difficulties.
It is an object of the present invention to provide alternative smoking article constructions without the disadvantages seen in the prior art documents, which constructions have the advantage of a reduced, or possibly negligible, inter-puff sidestream production, yet which can resume normal smoking characteristics when the article is drawn upon.
Cigarettes according to the present invention seek to use the tobacco material therein in a more effective manner, so that no tobacco or substantially less than the normal amount of tobacco is wasted in the inter-puff period.